feat: Auto-detect whether to use complete/streaming parser

[epage]

Previously in #6, I was transitioning parsers from returning FnMut(I) -> IResult<I, O, E> to structs that implement Parser so we could implement two unique parse traits, one for complete and one for streaming parsing. That ran into a series of problems, including not-as-great type inference.

This PR takes a different approach by making the type of parser a property of the Input, using const-generics. We can then specialize the implementation based on a const STREAMING: bool.

Potential downsides

• Intentionally mixing complete and streaming parsers due to complications with the error type
• Extra line noise for streaming users
  • I'm feeling like this will be acceptable as most of the noise is felt in tests and streaming is likely a less common case
• Output types not carrying Streaming<T> type
  • For nom::bytes, I automatically convert to the Complete type but that might not always be the most accurate.
  • Unspecialzied functions, like recognize, can't be specialized without adding a new trait bound
  • We might want a dedicated trait for this as it feels incorrect to use InputIsStreaming::Complete for something unrelated to Complete vs Streaming and to use that trait in non-specialized places

Steps

• Create context-sensitive streaming/complete parsers
• Migrate all code off of streaming/complete-specific parsers
• Deprecate streaming/complete-specific parsers
• Ensure Streaming documentation is sufficient
• Resolve anything else returning Incomplete (e.g. length_data)
• Constrain nom::combinator::complete to streaming (move to trait, deprecating old version?)
  • As shown by length_value, complete can be useful in InputIsStreaming agnostic code.

Fixes rust-bakery/nom#1535

[coveralls]

Pull Request Test Coverage Report for Build 3688759797

• 551 of 974 (56.57%) changed or added relevant lines in 16 files are covered.
• 19 unchanged lines in 7 files lost coverage.
• Overall coverage decreased (-2.6%) to 58.408%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/combinator/mod.rs	6	7	85.71%
src/bits/mod.rs	9	12	75.0%
src/number/complete.rs	2	5	40.0%
src/number/streaming.rs	2	5	40.0%
src/parser.rs	2	5	40.0%
src/bits/streaming.rs	26	32	81.25%
src/bytes/mod.rs	52	60	86.67%
src/bits/complete.rs	25	34	73.53%
src/character/complete.rs	58	68	85.29%
src/character/streaming.rs	44	67	65.67%

Files with Coverage Reduction	New Missed Lines	%
src/bytes/streaming.rs	1	50.92%
src/number/complete.rs	1	59.73%
src/character/streaming.rs	2	73.01%
src/number/streaming.rs	2	60.68%
src/bytes/complete.rs	3	66.86%
src/parser.rs	4	27.06%
src/lib.rs	6	0%

Totals
Change from base Build 3688567867:	-2.6%
Covered Lines:	1754
Relevant Lines:	3003

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💛 - Coveralls